1. Field of the Invention
The present invention relates to a transfer apparatus.
2. Description of the Related Art
Transfer apparatuses for transferring workpieces such as substrates are conventionally known (see e.g. JP-A 7-504128). FIG. 1 illustrates a conventional transfer apparatus. The illustrated transfer apparatus 900 is of the type called a “frog-leg” robot and has link arms 912-915, driving arms 917, 918, a base 919 and tables 925, 926.
The driving arms 917 and 918 are pivotally supported on the base 919. The base ends of the link arms 912 and 913 are pivotally connected to the respective driving arms 917 and 918. The front ends of the link arms 912 and 913 are connected to the table 925. Similarly, the base end of the link arm 914 and the base end of the link arm 915 are pivotally connected to the driving arm 917 and the driving arm 918, respectively. The front ends of the link arms 914 and 915 are connected to the table 926. Workpieces are transferred as placed on the tables 925, 926.
With the transfer apparatus 900 having such a structure, when the driving arms 917, 918 pivot relative to the base 919, the tables 925, 926 move forward or backward. FIG. 1 illustrates the apparatus 900 in its original posture. FIG. 2 illustrates the apparatus with the link arms 912 and 913 extended. The transfer apparatus 900 is configured to extend or retract the two pairs of link arms 912-915 with a small driving force, which is advantageous in terms of operation efficiency. For this purpose, the two pairs of link arms 912-915 are symmetrical with respect to a center line passing through the driving arms 917 and 918 in the original posture.
Generally, a transfer apparatus with a smaller rotation area is preferred. On the other hand, there is a demand for a transfer apparatus capable of transferring large workpieces. It may be considered necessary to increase the stroke of the extension/contraction movement of the tables 925, 926 to be able to transfer larger workpieces. The stroke of the extension/contraction movement of the table 925, 926 depends on the lengths of the link arms 912-915 and the lengths of the driving arms 917, 918. Thus, to increase the stroke of the extension/contraction movement, it may be considered necessary to increase the lengths of the arms 912-915 or the lengths of the driving arms 917, 918. However, when the lengths of the link arms 912-915 or the driving arms 917, 918 are increased, the rotation area of the transfer apparatus 900 inevitably increases.